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.\" $Id: gelf.3 3743 2019-06-12 19:36:30Z jkoshy $
.\"
.Dd October 23, 2020
.Dt GELF 3
.Os
.Sh NAME
.Nm gelf
.Nd class-independent API for ELF manipulation
.Sh LIBRARY
.Lb libelf
.Sh SYNOPSIS
.In gelf.h
.Sh DESCRIPTION
This manual page describes a class independent API for manipulating
ELF objects.
This API allows an application to operate on ELF descriptors without
needing to the know the ELF class of the descriptor.
.Pp
The GElf API may be used alongside the ELF API without restriction.
.Ss GElf Data Structures
The GElf API defines the following class-independent data structures:
.Bl -tag -width GElf_Sxword
.It Vt GElf_Addr
A representation of ELF addresses.
.It Vt GElf_Chdr
A class-independent representation of an ELF Compression Header.
.It Vt GElf_Dyn
A class-independent representation of ELF
.Sy .dynamic
section entries.
.It Vt GElf_Ehdr
A class-independent representation of an ELF Executable Header.
.It Vt GElf_Half
An unsigned 16 bit quantity.
.It Vt GElf_Off
A class-independent representation of a ELF offset.
.It Vt GElf_Phdr
A class-independent representation of an ELF Program Header Table
entry.
.It Vt GElf_Rel
A class-independent representation of an ELF relocation entry.
.It Vt GElf_Rela
A class-independent representation of an ELF relocation entry with
addend.
.It Vt GElf_Shdr
A class-independent representation of an ELF Section Header Table
entry.
.It Vt GElf_Sword
A signed 32 bit quantity.
.It Vt GElf_Sxword
A signed 64 bit quantity.
.It Vt GElf_Sym
A class-independent representation of an ELF symbol table entry.
.It Vt GElf_Word
An unsigned 32 bit quantity.
.It Vt GElf_Xword
An unsigned 64 bit quantity.
.El
.Pp
These data structures are sized to be compatible with the
corresponding 64 bit ELF structures, and have the same internal
structure as their 64 bit class-dependent counterparts.
Class-dependent ELF structures are described in
.Xr elf 5 .
.Ss GElf Programming Model
GElf functions always return a
.Em copy
of the underlying (class-dependent) ELF data structure.
The programming model with GElf is as follows:
.Bl -enum
.It
An application will retrieve data from an ELF descriptor using a
.Fn gelf_get_*
function.
This will copy out data into a private
.Vt GElf_*
data structure.
.It
The application will work with its private copy of the GElf
structure.
.It
Once done, the application copies the new values back to the
underlying ELF data structure using the
.Fn gelf_update_*
functions.
.It
The application will then use the
.Fn elf_flag*
APIs to indicate to the ELF library that an ELF data structure is dirty.
.El
.Pp
When updating an underlying 32 bit ELF data structure, the GElf
routines will signal an error if a GElf value is out of range
for the underlying ELF data type.
.Ss Namespace use
The GElf interface uses the following symbols:
.Bl -tag -width indent
.It GElf_*
Class-independent data types.
.It gelf_*
For functions defined in the API set.
.El
.Ss GElf Programming APIs
This section provides an overview of the GElf programming APIs.
Further information is provided in the manual page of each function
listed here.
.Bl -tag -width indent
.It "Allocating ELF Data Structures"
.Bl -tag -compact -width indent
.It Fn gelf_newehdr
Allocate a new ELF Executable Header.
.It Fn gelf_newphdr
Allocate a new ELF Program Header Table.
.El
.It "Data Translation"
.Bl -tag -compact -width indent
.It Fn gelf_xlatetof
Translate the native representation of an ELF data structure to its
file representation.
.It Fn gelf_xlatetom
Translate from the file representation of an ELF data structure to a
native representation.
.El
.It "Retrieving ELF Data"
.Bl -tag -compact -width indent
.It Fn gelf_getchdr
Retrieve an ELF Compression Header from the underlying ELF descriptor.
.It Fn gelf_getdyn
Retrieve an ELF
.Sy .dynamic
table entry.
.It Fn gelf_getehdr
Retrieve an ELF Executable Header from the underlying ELF descriptor.
.It Fn gelf_getphdr
Retrieve an ELF Program Header Table entry from the underlying ELF descriptor.
.It Fn gelf_getrel
Retrieve an ELF relocation entry.
.It Fn gelf_getrela
Retrieve an ELF relocation entry with addend.
.It Fn gelf_getshdr
Retrieve an ELF Section Header Table entry from the underlying ELF descriptor.
.It Fn gelf_getsym
Retrieve an ELF symbol table entry.
.El
.It Queries
.Bl -tag -compact -width indent
.It Fn gelf_checksum
Retrieves the ELF checksum for an ELF descriptor.
.It Fn gelf_fsize
Retrieves the size of the file representation of an ELF type.
.It Fn gelf_getclass
Retrieves the ELF class of an ELF descriptor.
.El
.It "Updating ELF Data"
.Bl -tag -compact -width ".Fn gelf_update_shdr"
.It Fn gelf_update_dyn
Copy back an ELF
.Sy .dynamic
Table entry.
.It Fn gelf_update_phdr
Copy back an ELF Program Header Table entry.
.It Fn gelf_update_rel
Copy back an ELF relocation entry.
.It Fn gelf_update_rela
Copy back an ELF relocation with addend entry.
.It Fn gelf_update_shdr
Copy back an ELF Section Header Table entry.
.It Fn gelf_update_sym
Copy back an ELF symbol table entry.
.El
.El
.Sh SEE ALSO
.Xr elf 3 ,
.Xr elf 5
.Sh HISTORY
The
.Nm
API first appeared in
.At V.4 .
This implementation of the API first appeared in
.Fx 7.0 .
.Sh AUTHORS
The GElf API was implemented by
.An Joseph Koshy Aq Mt jkoshy@FreeBSD.org .